Significance

In a study including 17 societies, we found that people are motivated to trust and cooperate more with their ingroup, than
harm the outgroup. Reputation-based indirect reciprocity may offset this ingroup favoritism, because we found that reputational
concern universally increases cooperation with both ingroup and outgroup members. We also found that people who are dispositionally
cooperative are less parochial and more universal in their cooperation. In a time of increasing parochialism in both domestic
and international relations, our findings affirm us of the danger of the strong human universal toward parochial altruism.
Yet, our findings suggest that in all societies, there exist people whose cooperation transcends group boundaries and provides
a solution to combating parochialism: reputation-based indirect reciprocity.

Abstract

International challenges such as climate change, poverty, and intergroup conflict require countries to cooperate to solve
these complex problems. However, the political tide in many countries has shifted inward, with skepticism and reluctance to
cooperate with other countries. Thus, cross-societal investigations are needed to test theory about trust and cooperation
within and between groups. We conducted an experimental study in 17 countries designed to test several theories that explain
why, who, and where people trust and cooperate more with ingroup members, compared with outgroup members. The experiment involved
several interactions in the trust game, either as a trustor or trustee. We manipulated partner group membership in the trust
game (ingroup, outgroup, or unknown) and if their reputation was at stake during the interaction. In addition to the standard
finding that participants trust and cooperate more with ingroup than outgroup members, we obtained findings that reputational
concerns play a decisive role for promoting trust and cooperation universally across societies. Furthermore, men discriminated
more in favor of their ingroup than women. Individual differences in cooperative preferences, as measured by social value
orientation, predicted cooperation with both ingroup and outgroup members. Finally, we did not find support for three theories
about the cross-societal conditions that influence the degree of ingroup favoritism observed across societies (e.g., material
security, religiosity, and pathogen stress). We discuss the implications for promoting cooperation within and between countries.